Materials 2014, 7, 7130-7144; doi:10.3390/ma7107130 OPEN ACCESS materials ISSN 1996-1944 www.mdpi.com/journal/materials Article Application of Various NDT Methods for the Evaluation of Building Steel Structures for Reuse Masanori Fujita * and Tomoya Masuda Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +81-836-85-9727; Fax: +81-836-85-9701. External Editor: Guillaume Habert Received: 11 June 2014; in revised form: 8 August 2014 / Accepted: 11 October 2014 / Published: 22 October 2014 Abstract: The reuse system proposed by the authors is an overall business system for realizing a cyclic reuse flow through the processes of design, fabrication, construction, maintenance, demolition and storage. The reuse system is one of the methods to reduce the environmental burden in the field of building steel structures. These buildings are assumed to be demolished within approximately 30 years or more for physical, architectural, economic and social reasons in Japan. In this paper, focusing on building steel structures used for plants, warehouses and offices without fire protection, the performance of steel structural members for reuse is evaluated by a non-destructive test. First, performance evaluation procedures for a non-destructive test, such as mechanical properties, chemical compositions, dimension and degradation, are shown. Tensile strengths are estimated using Vickers hardness measured by a portable ultrasonic hardness tester, and chemical compositions are measured by a portable optical emission spectrometer. The weldability of steel structural members is estimated by carbon equivalent and weld crack sensitivity composition using chemical compositions. Finally, the material grade of structural members of the building steel structure for reuse is estimated based on the proposed procedures. Keywords: steel structural member; reuse; mechanical properties; rolled section steel; non-destructive test; hardness; chemical composition Materials 2014, 7 7131 1. Introduction Based on the Fourth Assessment Report of IPCC, in order to reduce the amount of anthropogenic emissions to the same level as natural absorption, it is now widely accepted to set the goal of reducing global greenhouse gas emissions by 50% by the year 2050 [1,2]. Individual countries are making a full-fledged effort by putting forward mid- and long-term scenarios and visions to address global warming. Japan has set a long-term goal of reducing its CO2 emissions by 60%–80% from current levels by 2050. In order to achieve this goal, the Action Plan for Achieving a Low-carbon Society was approved in a Cabinet meeting. In 2009, based on the basic principles laid out in the charter of longer service life, natural symbiosis, energy conservation, resource conservation and cyclicity and succession, seventeen architecture-related organizations formulated “2050 Vision: Building-related Measures to Counteract Global Warming” to achieve carbon neutrality in this sector and to ultimately realize a low-carbon society [3,4]. As an architectural effort to reduce the global environmental burden, the authors have been pursuing studies on evaluating the environmental burden of building steel structures, focusing on the amount of waste and life cycle CO2 emissions and on a reuse system for steel products. Implementing any of the following measures can be effective at reducing the environmental burden in the life cycle of building steel structures: extending the service life of buildings themselves; reuse, which is extending service life at the structural member level; and recycling, which is extending service life at the material level; shown in Figure 1 [5,6]. Figure 1. Environmental performance and building structures. Building structure: ・Structural building level : Longevity ・Structural member level : Reuse of steel ・Structural material level : Recycle of steel Reduction of CO2 emissions The above scenarios illustrate that extending the service life of buildings is the most crucial element in reducing the environmental burden of building steel structures. Nevertheless, there are always a number of buildings that need to be demolished for physical, architectural, economic and social reasons. When such building steel structures have been demolished in the past, their structural members have been scrapped for recycling. Scrapping steel structural members for recycling requires energy for melting, and this melting process causes substantial CO2 emissions. However reusing structural members requires only ancillary energy for demolition, transportation and adjustments, causing less environmental burden, shown in Figure 2 [7–11]. Materials 2014, 7 7132 Figure 2. Steel structural members for reuse. Column Beam Reuse dismantling Steel, by nature, is the only type of structural member that can be refabricated. Even without special joints that facilitate demolition work, steel members can be reused after minor fabrication procedures, such as cutting, drilling and welding. Steel undergoes no major changes due to aging, except for rust and plasticization caused by large-scale earthquakes. Such excellent mechanical properties render steel suitable for reuse. Rust problems can be resolved by painting; plasticization caused by earthquakes can be handled by adopting damage-controlled design using a seismic design approach in which structural members are maintained within an elastic region by specifying seismic energy-absorbing members [12]. With respect to the performance evaluation of steel structural members for reuse, it is assumed that mechanical properties, such as tensile force, yield strength and elongation are generally evaluated by a destructive test. If test specimens can be obtained by building steel structures, it is possible to evaluate the performance by a destructive test. However, it is a difficulty to obtain a test specimen using building steel structures. Assuming building steel structures to be demolished approximately within 30 years or more, design specification and inspection certificates of building steel structures to be reused do not exist. This paper is aiming to evaluate the performance of steel members for reuse by a non-destructive test. First, the performance evaluation procedure of steel structural members for reuse is proposed. Furthermore, based on it, steel structural performances are evaluated if they meet the Japanese Industrial Standard. 2. Performance of Steel Structural Members by a Non-Destructive Test 2.1. Steel Structural Members for Reuse A reuse flow diagram of the building steel structure is presented in Figure 3. The dotted line shows the information flow, and the continuous line shows the flow of steel structural members for reuse. Steel structural members circulate via the database (DB) through a cyclic process: design, fabrication, construction, maintenance, dismantling and storage. The kinds of steel structural members for reuse are shown in Figure 4. The steel structural members for reuse in this study are the Japanese Industrial Standard (hereafter referred to as the JIS), such as rolled steels for general structures, rolled steel sections for welded structures and rolled steel for building structure. Bolts and other connecting materials, such as welding materials, are not included. Steel structural members for reuse are collected from non-fireproof factories, workplaces, warehouses and similar buildings pre-engineered mainly by steel manufacturers. Structural members to be reused are rolled section steels systematically sized and Materials 2014, 7 7133 manufactured in accordance with JIS. Here, steel structural members except, for the weld, are evaluated, since the ductility of steel structural members varies depending on construction quality and connection detail. Figure 3. Reuse flow. Design Storage Access Information management Fabrication Dismantling Registration ＤＢ Information Steel structural members for reuse Information Information management management Maintenance DB:Data base Construction Figure 4. Steel structural members for reuse. Steel structural members for reuse - Newly manufactured members Members obtained by careful Members obtained by careful without inspection certificate dismantling dismantling in the near future - Surplus members - Short members 2.2. Non-Destructive Test Destructive tests of metallic materials, such as the tensile test, indentation test and Charpy pendulum impact test, are used to evaluate steel structural performances. On the other hand, dimensional inspection, indentation test, chemical composition test and degradation inspection can be used to evaluate structural performance as non-destructive tests. The detection of cracks in weldments using ultrasonic testing is generally used in building steel structures [13,14]. Otherwise, a method for structural parameter identification utilizing elemental strain measurement is used and successfully verified at the element level [15]. Particularly, an ultrasonic hardness tester is used in processed goods, metal molds and measuring the strength of steel sections, and it can easily measure the hardness index of materials, from the measurement of equivalent stiffness by an ultrasonic vibrator sensor, without measuring the plastic deformation [16]. A portable optical emission spectrometer is used to measure their chemical compositions in plant piping and scrap materials as a non-destructive